Solid-state lighting apparatus and methods using energy storage

ABSTRACT

An apparatus includes a current control circuit configured to selectively provide current responsive to a varying voltage to at least one LED coupled in series with the first current control circuit and to at least one capacitor coupled to the at least one LED and the first current control circuit. The current control circuit may be configured to cause the at least one capacitor to be selectively charged from a current source and to be discharged via the at least one LED responsive to a varying input, such as a varying current from the current source or a varying voltage applied to the current source. For example, the current control circuit may be configured to limit current through the at least one LED to less than a current provided by the current source.

FIELD

The present inventive subject matter relates to lighting apparatus andmethods and, more particularly, to solid-state lighting apparatus andmethods.

BACKGROUND

Solid-state lighting arrays are used for a number of lightingapplications. For example, solid-state lighting panels including arraysof solid-state light emitting devices have been used as directillumination sources, for example, in architectural and/or accentlighting. A solid-state light emitting device may include, for example,a packaged light emitting device including one or more light emittingdiodes (LEDs), which may include inorganic LEDs, which may includesemiconductor layers forming p-n junctions and/or organic LEDs (OLEDs),which may include organic light emission layers.

Solid-state lighting arrays are used for a number of lightingapplications. For example, solid-state lighting panels including arraysof solid-state light emitting devices have been used as directillumination sources, for example, in architectural and/or accentlighting. Solid-state lighting devices are also used in lightingfixtures, such as incandescent bulb replacement applications, tasklighting, recessed light fixtures and the like. For example, Cree, Inc.produces a variety of recessed downlights, such as the LR-6 and CR-6,which use LEDs for illumination. Solid-state lighting panels are alsocommonly used as backlights for small liquid crystal display (LCD)screens, such as LCD display screens used in portable electronicdevices, and for larger displays, such as LCD television displays.

A solid-state light emitting device may include, for example, a packagedlight emitting device including one or more light emitting diodes(LEDs). Inorganic LEDs typically include semiconductor layers formingp-n junctions. Organic LEDs (OLEDs), which include organic lightemission layers, are another type of solid-state light emitting device.Typically, a solid-state light emitting device generates light throughthe recombination of electronic carriers, i.e. electrons and holes, in alight emitting layer or region.

Some attempts at providing solid-state lighting sources have involveddriving an LED or string or group of LEDs using a rectified AC waveform.However, because the LEDs require a minimum forward voltage to turn on,the LEDs may turn on for only a part of the rectified AC waveform, whichmay result in visible flickering, may undesirably lower the power factorof the system, and/or may increase resistive loss in the system.Examples of techniques for driving LEDs with a rectified AC waveform aredescribed in U.S. Patent Application Publication No. 2010/0308738 and incopending U.S. patent application Ser. No. 12/777,842 (Attorney DocketNo. 5308-1188, filed May 7, 2010), the latter of which is commonlyassigned to the assignee of the present application.

Other attempts at providing AC-driven solid-state lighting sources haveinvolved placing LEDs in an anti-parallel configuration, so that half ofthe LEDs are driven on each half-cycle of an AC waveform. However, thisapproach requires twice as many LEDs to produce the same luminous fluxas using a rectified AC signal.

SUMMARY

Some embodiments provide an apparatus including a first current controlcircuit configured to selectively provide current from a current sourceto at least one LED coupled in series with the first current controlcircuit and to at least one capacitor coupled to the at least one LEDand the first current control circuit. The first current control circuitmay be configured to cause the at least one capacitor to be selectivelycharged from the current source and to be discharged via the at leastone LED responsive to a varying input, such as a varying voltage orcurrent. For example, the first current control circuit may beconfigured to limit current through the at least one LED to less than acurrent provided by the current source.

In some embodiments, the apparatus may further include a second currentcontrol circuit configured to be coupled to a voltage source andconfigured to provide current to the at least one LED and to the atleast one storage capacitor. The first current control circuit and thesecond current control circuit may be configured to cause the at leastone capacitor to provide current to the at least one LED when a voltageof the voltage source is insufficient to forward-bias the at least oneLED. The second current control circuit may include a current sourcecircuit or a current sink circuit.

In some embodiments, the apparatus may further include a voltageregulator circuit configured to limit a voltage across the at least onecapacitor.

In some embodiments, the first current control circuit may include acurrent limiter circuit. For example, the first current control circuitmay include a current mirror circuit.

In additional embodiments, the apparatus may further include at leastone bypass circuit configured to bypass at least one of a plurality ofLEDs. The at least one bypass circuit may be configured to bypass atleast one of the plurality of LEDs responsive to the varying input.

Some embodiments provide a lighting apparatus including a current sourcecircuit, at least one LED coupled to an output of the current sourcecircuit, at least one capacitor coupled to the output of the currentsource circuit and a current limiter circuit configured to limit acurrent through the at least one LED to less than a current produced bythe current source circuit. The apparatus may further include arectifier circuit having an input configured to be coupled to an ACpower source and an output configured to be coupled to an input of thecurrent source circuit. The at least one LED may include a plurality ofLEDs, and the apparatus further includes at least one bypass circuitconfigured to bypass at least one of the plurality of LEDs.

Additional embodiments provide a lighting apparatus including a currentsource circuit, at least one first LED coupled to an output of thecurrent source circuit, at least one capacitor coupled to the output ofthe current source circuit and a current limiter circuit configured tolimit a current through the at least one LED to less than a currentproduced by the current source circuit. The apparatus further includes aplurality of second LEDs coupled in series with the current limitercircuit and the at least one first LED and bypass circuitry configuredto selectively bypass the second LEDs responsive to a varying voltageapplied to an input of the current source circuit.

In still further embodiments, a lighting apparatus includes at least oneLED and a current control circuit configured to provide current to theat least one LED from a power source that produces a periodicallyvarying voltage. The current control circuit is configured to cause theat least one LED to produce a light output that comprises clippednonzero troughs coinciding with nulls of the varying voltage. In someembodiments, the light output may have a frequency no greater than twicea frequency of the varying voltage. The troughs may be maintained atabout 5% or more of a peak level of the light output.

In some embodiments, the current control circuit may be configured totransfer energy from the power source to the at least one capacitorduring a portion of a period of the varying voltage and from the atleast one capacitor to the at least one LED near the nulls of thevarying voltage.

In further embodiments, a lighting apparatus includes at least one LEDand a current control circuit configured to provide current to the atleast one LED and to at least one capacitor from a power source thatproduces an AC voltage. Energy is transferred from the power source tothe at least one capacitor during a portion of a period of the ACvoltage and transferred from the at least one capacitor to the at leastone LED near zero crossings of the AC voltage. The light output may beconstrained to have a minimum level of at least 5% of a peak level ofthe light output.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the inventive subject matter and are incorporated inand constitute a part of this application, illustrate certainembodiment(s) of the inventive subject matter. In the drawings:

FIG. 1 illustrates a lighting apparatus according to some embodiments;

FIG. 2 illustrates a lighting apparatus according to furtherembodiments;

FIGS. 3A-B illustrate operations of a lighting apparatus according tosome embodiments;

FIG. 4 illustrates a lighting apparatus according to furtherembodiments;

FIG. 5 illustrates a current mirror circuit for a lighting apparatusaccording to some embodiments;

FIG. 6 illustrates a current control circuit for a lighting apparatusaccording to further embodiments;

FIG. 7 illustrates a current source circuit for a lighting apparatusaccording to some embodiments;

FIG. 8 illustrates a lighting apparatus according to furtherembodiments;

FIG. 9 illustrates a lighting apparatus configured to be coupled to atleast one external capacitor according to some embodiments;

FIG. 10 illustrates a driver device configured to be coupled to at leastone LED and at least one capacitor according to some embodiments;

FIG. 11 illustrates driver device with bypass circuitry according tosome embodiments;

FIG. 12 illustrates a lighting apparatus with an external capacitorconnection according to further embodiments;

FIG. 13 illustrates a lighting apparatus for use with a time-varyingcurrent source according to further embodiments;

FIG. 14 illustrates a lighting apparatus according to furtherembodiments;

FIG. 15 illustrates voltage, current and light output characteristics ofthe lighting apparatus of FIG. 14; and

FIGS. 16 and 17 illustrate current waveforms of lighting apparatuspowered by switchmode power supply circuitry.

DETAILED DESCRIPTION

Embodiments of the present inventive subject matter now will bedescribed more fully hereinafter with reference to the accompanyingdrawings, in which embodiments of the inventive subject matter areshown. This inventive subject matter may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the inventive subject matter to those skilled in theart. Like numbers refer to like elements throughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present inventivesubject matter. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

It will be understood that when an element or layer is referred to asbeing “on” another element or layer, the element or layer can bedirectly on another element or layer or intervening elements or layersmay also be present. In contrast, when an element is referred to asbeing “directly on” another element or layer, there are no interveningelements or layers present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

Spatially relative terms, such as “below”, “beneath”, “lower”, “above”,“upper”, and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation, in addition to theorientation depicted in the figures. Throughout the specification, likereference numerals in the drawings denote like elements.

Embodiments of the inventive subject matter are described herein withreference to plan and perspective illustrations that are schematicillustrations of idealized embodiments of the inventive subject matter.As such, variations from the shapes of the illustrations as a result,for example, of manufacturing techniques and/or tolerances, are to beexpected. Thus, the inventive subject matter should not be construed aslimited to the particular shapes of objects illustrated herein, butshould include deviations in shapes that result, for example, frommanufacturing. Thus, the objects illustrated in the figures areschematic in nature and their shapes are not intended to illustrate theactual shape of a region of a device and are not intended to limit thescope of the inventive subject matter.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinventive subject matter. As used herein, the singular forms “a”, “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” “comprising,” “includes” and/or “including” whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this present inventive subjectmatter belongs. It will be further understood that terms used hereinshould be interpreted as having a meaning that is consistent with theirmeaning in the context of this specification and the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein. The term “plurality” is used herein torefer to two or more of the referenced item.

The expression “lighting apparatus”, as used herein, is not limited,except that it indicates that the device is capable of emitting light.That is, a lighting apparatus can be a device which illuminates an areaor volume, e.g., a structure, a swimming pool or spa, a room, awarehouse, an indicator, a road, a parking lot, a vehicle, signage,e.g., road signs, a billboard, a ship, a toy, a mirror, a vessel, anelectronic device, a boat, an aircraft, a stadium, a computer, a remoteaudio device, a remote video device, a cell phone, a tree, a window, anLCD display, a cave, a tunnel, a yard, a lamppost, or a device or arrayof devices that illuminate an enclosure, or a device that is used foredge or back-lighting (e.g., back light poster, signage, LCD displays),bulb replacements (e.g., for replacing AC incandescent lights, lowvoltage lights, fluorescent lights, etc.), lights used for outdoorlighting, lights used for security lighting, lights used for exteriorresidential lighting (wall mounts, post/column mounts), ceilingfixtures/wall sconces, under cabinet lighting, lamps (floor and/or tableand/or desk), landscape lighting, track lighting, task lighting,specialty lighting, ceiling fan lighting, archival/art display lighting,high vibration/impact lighting, work lights, etc., mirrors/vanitylighting, or any other light emitting device.

The present inventive subject matter further relates to an illuminatedenclosure (the volume of which can be illuminated uniformly ornon-uniformly), comprising an enclosed space and at least one lightingapparatus according to the present inventive subject matter, wherein thelighting apparatus illuminates at least a portion of the enclosed space(uniformly or non-uniformly).

Some embodiments of the inventive subject matter arise from arealization that flicker in an AC-driven LED lighting apparatus may bereduced by using a capacitor to store energy near peak voltage and usingthe stored energy to drive the LED(s) when the input AC voltagemagnitude is less than required to forward bias the LED(s). In someembodiments, a current control circuit, for example, a current limitercircuit, is coupled in series with one or more LEDs. A storage capacitormay be coupled to the one or more LEDs. The current limiter circuit maybe configured to direct current to the storage capacitor under certaininput voltage conditions such that energy stored in the storagecapacitor may be discharged via the one or more LEDs under other inputvoltage conditions. Thus, more uniform illumination may be achieved.

FIG. 1 illustrates a lighting apparatus 100 according to someembodiments. The apparatus 100 includes one or more LEDs 110. The one ormore LEDs 110 may, for example, comprise a string of LEDs of a single ormultiple colors. The one or more LEDs 110 may include, for example, aserial string of LEDs, serial combinations of paralleled LEDs orcombinations thereof. The apparatus 100 may further include additionalcircuitry associated with the one or more LEDs 110, such as temperatureand/or color compensation circuitry. Examples of compensation circuitrythat may be used with LEDs are described in U.S. patent application Ser.No. 12/704,730 (Attorney Docket No. 5308-1128IP, filed Feb. 12, 2010),commonly assigned to the assignee of the present application andincorporated herein by reference.

The one or more LEDs 110 are coupled in series with the first currentcontrol circuit 120. One or more storage capacitors 130 may be coupledin parallel with the one or more LEDs 110 and the first current controlcircuit 120. The one or more storage capacitors 130 may include, forexample, one or more electrolytic capacitors, ceramic capacitors, filmcapacitors, super-capacitors, ultra-capacitors and/or combinationsthereof.

A second current control circuit 140 is coupled in series with theparallel combination of the one or more LEDs' 110, the first currentcontrol circuit 120 and the one or more storage capacitors 130. Thefirst current control circuit 120 and the second current control circuit140 are configured such that, in responsive to a time-varying voltage ν,the one or more storage capacitors 130 are charged via the secondcurrent control circuit 140 and then discharged via the one or more LEDsresponsive to the varying voltage ν.

FIG. 2 illustrates an example of a lighting apparatus 200 along thelines described above. The lighting apparatus 200 includes one or moreLEDs 210 coupled in series with a current limiter circuit 220, and oneor more storage capacitors 230 coupled in parallel with the one or moreLEDs 210 and the current limiter circuit 220. The one or more LEDs 210may be configured in a number of different ways and may have variouscompensation circuits associated therewith, as discussed above withreference to the one or more LEDs 110 of FIG. 1. A current sourcecircuit 240 is coupled to an output of a rectifier circuit 250 thatproduces a time-varying voltage ν, e.g., a full-or-half wave rectifiedvoltage, from an AC input. The current source circuit 240 provides acontrolled current to the parallel combination of the one or morestorage capacitors 230 and the one or more LEDs 210 and the currentlimiter circuit 220. The current limiter circuit 220 may be configuredto limit current through the one or more LEDs 210 to a value less than acurrent provided by the current source circuit 240 such that current isdiverted to the one or more storage capacitors 230, with the storedenergy used to drive the one or more LEDs 210 in reduced-magnitudeportions of the input AC voltage waveform.

This is further illustrated in FIG. 3A, where it is assumed that the ACinput has a sinusoidal voltage waveform 310 and the rectifier circuit250 is a full-wave rectifier. During a time interval T1, the currentlimiter circuit 220 limits the current i₂ through the one or more LEDs210 to a value less than the total current i₁ supplied by the currentsource circuit 240. During this period, current flows to one or morestorage capacitors 230, thus charging the one or more capacitors 230.During an interval T2 in which the magnitude of the rectifier outputvoltage ν falls below a certain level, the current i₂ through the one ormore LEDs 210 is maintained by discharging the one or more storagecapacitors 230. In this manner, the one or more LEDs 210 may continue tobe illuminated, thus potentially reducing flicker in comparison toconventional AC drive circuits that shut off LED conduction forsignificant portions of the rectified AC waveform. As illustrated inFIG. 3B, the arrangement illustrated in FIG. 2 may be advantageous forapplications using phase cut dimming. In particular, the AC input to therectifier circuit 250 may be a phase cut AC signal (e.g., one generatedfrom a conventional dimmer) having a phase-cut AC waveform 310′. Theillumination produced by the one or more LEDs 210 may be reduced inproportion to the amount of phase cut, while the combined action of thecurrent source circuit 240, the current limiter circuit 220 and the oneor more storage capacitors 230 can reduce flicker by maintaining currentthrough the one or more LEDs 210 during reduced-magnitude portions ofthe input AC waveform 310′. It will be appreciated that the voltage andcurrent waveforms illustrated in FIGS. 3A and 3B are idealized forpurposes of illustrations, and that waveforms exhibited by variouspractical embodiments may deviate therefrom depending, for example, oncharacteristics of the type of current source and current limit circuitsused and/or properties of circuit components (e.g., transistors,capacitors, etc.) used in the circuitry.

It will be further understood that, although FIG. 2 illustrates use of acurrent source circuit 240 coupled between the output of a rectifiercircuit 250 and one or more LEDs 210 and one or more storage capacitors230, a current control circuit providing similar functionality may becoupled elsewhere. For example, the current source circuit 240 may bereplaced by a current control circuit positioned at the input of therectifier circuit 250 that controls current produced by the rectifiercircuit 250.

FIG. 4 illustrates a lighting apparatus 400 along the lines discussedabove with reference to FIG. 2. The apparatus 400 includes one or moreLED's 410 coupled in series with a current mirror circuit 420. The oneor more LEDs 410 may be configured in a number of different ways and mayhave various compensation circuits associated therewith, as discussedabove with reference to the one or more LEDs 110 of FIG. 1. One or morestorage capacitors are coupled in parallel with the one or more LEDs 410and the current mirror circuit 420. A current source circuit 440includes a resistor R coupled to the parallel combination of the one ormore storage capacitors 430 and the one or more LEDs 410 and the currentmirror circuit 420. The current source circuit 440 is also coupled to afull-wave rectifier circuit 450, which includes diodes D1-D4. Thecurrent mirror circuit 420 may be configured to limit current throughthe one or more LEDs 410 to a level less than a nominal current producedby the current source circuit 440. In this manner, the one or morestorage capacitors 430 may be alternately charged via the current sourcecircuit 440 and discharged via the one or more LEDs 410, thusmaintaining more uniform illumination.

FIG. 5 illustrates an example of current mirror circuit 420′ that may beused in the apparatus 400 of FIG. 4, including first and secondtransistors Q1, Q2 and resistors R1, R2, R3 connected in a currentmirror configuration. The current limit circuit 420′ may provide acurrent limit of approximately (V_(LED)−0.7)/(R1+R2)×(R2/R3). A voltagelimiter circuit 460, e.g., a zener diode, may also be provided to limitthe voltage developed across the one or more storage capacitors 430.

It will be appreciated that any of a wide variety of circuits may beused for current control in a lighting apparatus along the linediscussed above. FIG. 6 illustrates an example of a current limitercircuit 220′ that may be used, for example, in the circuit arrangementof FIG. 2. The current limiter circuit 220′ includes an amplifier U thatgenerates a drive signal for a transistor Q coupled in series with oneor more LEDs 210. The amplifier U generates the transistor drive signalresponsive to a comparison of a reference voltage V_(ref) to a currentsense signal generated by a current sense resistor R coupled in serieswith the one or more LEDs and the transistor Q.

Similarly, a wide variety of different circuit may be used for a currentsource for an LED/capacitor load. For example, FIG. 7 illustrates acurrent source circuit 240′ that may be used in the circuit arrangementof FIG. 2. The current source circuit 240′ includes transistors Q1, Q2and resistors R1, R2, R3 arranged in a current mirror configuration.

According further embodiments, capacitive energy storage techniques asdiscussed above may be combined with techniques in which LEDs areincrementally switched on and off in response to a varying inputvoltage, such as a rectified AC waveform. For example, theaforementioned U.S. patent application Ser. No. 12/775,842 describeslighting apparatus in which LEDs in string are selectively bypassed inresponse to a varying voltage waveform. Such bypass circuitry may becombined with capacitive storage techniques along the lines discussedabove.

FIG. 8 illustrates an example of such a combination. A lightingapparatus 800 includes one or more LEDs 810 coupled in series with afirst current control circuit 820, with one or more storage capacitors830 coupled in parallel with the one or more LEDs 810 and the firstcurrent control circuit 820.

A second current control circuit 840 is coupled in series with thesecomponents, along with a string 850 of additional LEDs. The string 850may be arranged in groups 850 a, 850 b, 850 c, . . . , 850 i, which maybe selectively bypassed using bypass circuits 860 a, 860 b, 860 c, . . .860 i. The groups 850 a, 850 b, 850 c, . . . , 850 i may each includeone or more LEDs, which may be connected in various parallel and/orserial ways. Responsive to a varying input voltage ν (e.g., a full-waverectified waveform produced by a rectifier), the bypass circuits 860 a,860 b, 860 c, . . . 860 i may operate such that the groups 850 a, 850 b,850 c, . . . , 850 i of LEDs are incrementally coupled in series withthe one or more LEDs 810 as the magnitude of the input voltage νincreases. The first and second current control circuit 820, 840 may beconfigured such that current is eventually diverted to the one or morestorage capacitors at or near the peak of the input voltage ν. As themagnitude of the input voltage ν decreases, the groups 850 a, 850 b, 850c, . . . , 850 i of LEDs are incrementally bypassed. When the magnitudeof the input voltage ν approaches its minimum, current may be dischargedfrom the one or more storage capacitors 830 through the one or more LEDs810 to maintain illumination until the magnitude of the input voltage νagain increases.

It will be understood that the apparatus 800 of FIG. 8 is provide as anexample for purposes of explanation, and that a variety of other bypasscircuit arrangements may be used. For example, bypass circuitry may beused to bypass individual segments of a string of LEDs, rather than theshunt arrangement shown in FIG. 8. Other arrangements may includereversed arrangements of the circuit shown in FIG. 8, e.g., theenergy-storing component may be connected at the “bottom” of the LEDstring, rather than the “top” side arrangement illustrated in FIG. 8.

It will also be appreciated that embodiments of the inventive subjectmay have any of a variety of physical arrangements, e.g., differentarrangements of circuit components and/or packaging of such components.For example, some embodiments may provide a lighting apparatus with bothintegrated driver circuitry (e.g., current source and limit circuits)and storage capacitance. Further embodiments may provide lightingapparatus with provision for connection to external storage capacitance.Some embodiments may provide a driver device configured to be coupled toone or more LEDs and to one or more external storage capacitors. Stillfurther embodiments may include bypass circuitry and/or voltage sourcecircuitry, such as a rectifier circuit.

FIG. 9 illustrates a lighting apparatus 900 according to someembodiments. The lighting apparatus 900 includes first and secondcurrent control circuits 120, 140 and one or more LEDs 110, along linesdiscussed above. The apparatus 900 further includes a port 910configured to be coupled to one or more external storage capacitors.FIG. 10 illustrates a device 1000, e.g., an integrated circuit, circuitmodule or the like, including first and second current control circuits120, 140 along lines discussed above. The device 1000 includes ports1010, 1020 configured to be coupled to one or more LEDs 110 and one ormore storage capacitors 130 external to the device 1000. FIG. 11illustrates a device 1100 including first and second current controlcircuits 120, 140, along with one or more bypass circuits 860 a, 860 b,860 c, . . . , 860 i along lines discussed above with reference to FIG.8. The device 1100 includes ports 1110, 1120, 1130 configured to becoupled to one or more LEDs 110 and one or more storage capacitors 130external to the device 1100.

FIG. 12 illustrates a lighting apparatus 1200 including first and secondcurrent control circuits 120, 140, one or more LEDs 110 and one or morestorage capacitors 130, along with an integrated rectifier circuit 150.It will be appreciated that a rectifier or other voltage source circuitmay be similarly integrated in the devices illustrated in FIGS. 9-11.

According to further embodiments, a lighting apparatus utilizing energystorage techniques similar to those discussed above may be used withcurrent source that provides a time-varying current. For example, asillustrated in FIG. 13, a lighting apparatus 1300 may include one ormore LEDs 1310 coupled in series with a current limiter circuit 1320,and one or more storage capacitors 1330 coupled in parallel with the oneor more LEDs 1310 and the current limiter circuit 1320. The apparatus1300 may be configured to be coupled to a current source circuit 20 thatproduces a time-varying output current i, which may be an AC current ora DC current. The current limiter circuit 1320 may be configured tolimit current through the one or more LEDs 1310 to a value less than apeak value of the time-varying current i such that current is divertedto charge the one or more storage capacitors 1330 when the time-varyingcurrent i exceeds the current limit of the current limiter circuit 1320.When the time-varying current i decreases below the current limit,current may be delivered from the one or more storage capacitors 1330 tothe one or more LEDs 1310 to maintain a given level of illumination. Thecurrent limiter circuit 1320 may take the form, for example, of thecurrent limiter circuitry illustrated in FIG. 5. Additional circuitry,such as the voltage limiting circuitry illustrated in FIG. 5 and/or thebypass circuitry illustrated in FIG. 8, may also be included in theapparatus 1300. Some embodiments may use circuitry along the linesillustrated in FIG. 13, but with provision of one or more ports forconnection of external LEDs and/or storage capacitors, along the linesdiscussed above with reference to FIGS. 9-12.

According to further embodiments, a light output from an AC powered LEDlighting apparatus may be “valley filled” using, for example, techniquesalong the lines discussed above, so that perceptible flicker may bereduced or eliminated. In particular, a periodic light output with“clipped” troughs near the zero crossings of an AC power input may beobtained by using a storage capacitor to provide current to at least oneLED during time periods near the zero crossings. Using techniques alongthe lines described above, cycling of the storage capacitor may belimited to twice the AC voltage frequency (e.g., 120 Hz for a 60 Hz ACpower source), such that reliability of the storage capacitor may beimproved in comparison to the reliability of storage capacitors used indesigns that use, for example, switch mode power supplies that operateat 10 kHz or greater.

FIG. 14 illustrates a lighting apparatus 1400 according to furtherembodiments, while FIG. 15 illustrates voltage, current and light outputcharacteristics of the apparatus 1400. The apparatus 1400 includes astring of serially-connected sets 1410 a, 1410 b, 1410 c of LEDs. Arectifier circuit 1450 is configured to receive power from a powersource, which provides an AC voltage ν_(AC), and to produce a full-waverectified output current i_(R). A storage capacitor 1430 is coupled tothe first set 1410 a of at least one LED. A current limiter circuit 1420is configured to limit current flowing through a first set 1410 a of oneor more LEDs. The current limiter circuit 1420 is a dual of the circuitillustrated in FIG. 5, and includes transistors Q1, Q2 and resistors R1,R2, R3. A zener diode DZ provides overvoltage protection. A currentcontrol circuit 1440 provides selective bypassing of the sets 1410 b,1410 c of LEDs. This current control circuit 1440 may take any of anumber of different forms, and generally may operate to bypass the sets1410 a, 1410 b such that the sets 1410 b, 1410 c are incrementally addedand removed from series connection with the first set 1410 as therectified voltage produced by the rectifier circuit 1450 increases anddecreases. This operation results in a “stepped” current waveform forthe input current i_(R), as illustrated in FIG. 15.

As further illustrated in FIG. 15, a periodic light output 1500 is thusproduced by the apparatus 1400. During a first portion T₁ of a period Tof the light output 1500, the light output generally tracks the ACvoltage ν_(AC), with the storage capacitor 1430 being charged at andnear the magnitude peaks of the AC voltage ν_(AC). During a secondportion T₂ of the period T, the light output 1500 is “clipped” (held up)to a level that is at least 5% of the peak light output level at bytransfer of stored charge from the storage capacitor 1430 to the firstset 1410 a of at least one LED such that a non-zero light output levelis maintained at nulls (e.g., zero crossings) of the AC voltage ν_(AC).Although perception of flicker in lighting is generally dependent on theobserver, it is believed that maintaining a minimum light output levelof at least 5-10% of the maximum light output level renders flickernegligibly perceptible.

As shown in FIGS. 16 and 17, the LED current waveforms produced bydifferent types of switch-mode power supply circuits in off-line LEDsystems produce a similar light output (waveform) which typically doesnot create visible flicker but at the expense of complex and costlycircuitry. A switch-mode power supply LED driver also typically needs anelectromagnetic interference (EMI) filter to comply with stringent FCCor similar regulatory agency limits. A potential advantage of circuitssuch as the one illustrated in FIG. 14 is that there may be no need foran EMI filter as there is no high-frequency switching. Another potentialadvantage is that the storage capacitor 1430 is cycled(charged/discharged) at a relatively low rate and lower RMS currentlevels in comparison to the high cycle rates and high RMS currentstypically experienced by storage capacitors used in conventionalswitch-mode power supply circuits, thus potentially improvingreliability and useful lifetime and/or enabling the use of lessexpensive storage capacitors. These features may be particularlyvaluable in solid-state lighting applications, in which low cost andhigh reliability are distinct advantages.

In off-line LED systems which do not use switch-mode power supplies asLED drivers, such as AC LED systems with only a rectifier and a currentlimiting resistor, the light output typically falls to at or near zerowhen the input voltage falls below the level of the LED string voltage,which may cause visible flicker at twice the line frequency. In some ACLED systems that use multiple switched LED segments and no energystorage, the light output may stay at zero for a shorter duration thannon-segmented AC LED systems, but still may cause visible flicker. Suchflicker may be more prominent and perceptible when objects are movingaround or back and forth in the presence of such a light, as human eyestend to be more sensitive to sudden changes in light level, such asgoing completely dark, and less sensitive to gradual changes. Someembodiments of the inventive subject matter, such as in the lightingapparatus of FIG. 14, may produce a light output that does not go tozero using a “valley fill” or “light fill” technique without thecomplexity of using a switch-mode power supply.

In the drawings and specification, there have been disclosed typicalembodiments of the inventive subject matter and, although specific termsare employed, they are used in a generic and descriptive sense only andnot for purposes of limitation, the scope of the inventive subjectmatter being set forth in the following claims.

What is claimed is:
 1. An apparatus comprising: a first current controlcircuit configured to selectively provide current from a current sourceto at least one LED coupled in series with the first current controlcircuit and to at least one capacitor coupled to the at least one LEDand the first current control circuit.
 2. The apparatus of claim 1,wherein the first current control circuit is configured to cause the atleast one capacitor to be selectively charged from the current sourceand to be discharged via the at least one LED responsive to a varyinginput.
 3. The apparatus of claim 2, wherein the first current controlcircuit is configured to limit current through the at least one LED toless than a current provided by the current source.
 4. The apparatus ofclaim 2, further comprising a second current control circuit configuredto be coupled to a voltage source and configured to provide current tothe at least one LED and to the at least one storage capacitor.
 5. Theapparatus of claim 4, wherein the first current control circuit and thesecond current control circuit are configured to cause the at least onecapacitor to provide current to the at least one LED when a voltage ofthe voltage source is insufficient to forward-bias the at least one LED.6. The apparatus of claim 4, wherein the second current control circuitcomprises a current source circuit or a current sink circuit.
 7. Theapparatus of claim 4, further comprising the voltage source.
 8. Theapparatus of claim 7, wherein the voltage source comprises a rectifiercircuit.
 9. The apparatus of claim 1, further comprising a voltageregulator circuit configured to limit a voltage across the at least onecapacitor.
 10. The apparatus of claim 1, wherein the first currentcontrol circuit comprises a current limiter circuit.
 11. The apparatusof claim 1, wherein the first current control circuit comprises acurrent mirror circuit.
 12. The apparatus of claim 1, further comprisinga port configured to be coupled to the at least one LED.
 13. Theapparatus of claim 1, further comprising the at least one LED.
 14. Theapparatus of claim 1, further comprising a port configured to be coupledto the at least one capacitor.
 15. The apparatus of claim 1, furthercomprising the at least one capacitor.
 16. The apparatus of claim 1,wherein the apparatus further comprises at least one bypass circuitconfigured to bypass at least one of a plurality of LEDs.
 17. Theapparatus of claim 16, wherein the at least one bypass circuit isconfigured to bypass at least one of the plurality of LEDs responsive tothe varying input.
 18. The apparatus of claim 16, further comprising atleast one port configured to be coupled to the plurality of LEDs. 19.The apparatus of claim 16, further comprising the plurality of LEDs. 20.A lighting apparatus comprising: a current source circuit; at least oneLED coupled to an output of the current source circuit; at least onecapacitor coupled to the output of the current source circuit; and acurrent limiter circuit configured to limit a current through the atleast one LED to less than a current produced by the current sourcecircuit.
 21. The apparatus of claim 20, wherein the current sourcecircuit and the current limiter circuit are configured to cause the atleast one capacitor to be selectively charged via the current sourcecircuit and discharged via the at least one LED responsive to a varyingvoltage applied to an input of the current source circuit.
 22. Theapparatus of claim 21, further comprising a rectifier circuit having aninput configured to be coupled to an AC power source and an outputconfigured to be coupled to an input of the current source circuit. 23.The apparatus of claim 21, wherein the current limiter circuit comprisesa current mirror circuit coupled in series with the at least one LED.24. The apparatus of claim 21, wherein the at least one LED comprises aplurality of LEDs, wherein the apparatus further comprises at least onebypass circuit configured to bypass at least one of the plurality ofLEDs.
 25. A lighting apparatus comprising: a current source circuit; atleast one first LED coupled to an output of the current source circuit;at least one capacitor coupled to the output of the current sourcecircuit; a current limiter circuit configured to limit a current throughthe at least one LED to less than a current produced by the currentsource circuit; a plurality of second LEDs coupled in series with thecurrent limiter circuit and the at least one first LED; and bypasscircuitry configured to selectively bypass the second LEDs responsive toa varying voltage applied to an input of the current source circuit. 26.The apparatus of claim 25, wherein the current source circuit and thecurrent limiter circuit are configured to cause the at least onecapacitor to be selectively charged via the current source circuit anddischarged via the at least one first LED responsive to the varyingvoltage.
 27. A lighting apparatus comprising: at least one LED; and acurrent control circuit configured to provide current to the at leastone LED from a power source that produces a periodically varyingvoltage, the current control circuit configured to cause the at leastone LED to produce a light output that comprises clipped non-zerotroughs coinciding with nulls of the varying voltage.
 28. The apparatusof claim 27, wherein the troughs are maintained at about 5% or more of apeak level of the light output.
 29. The apparatus of claim 27, whereinthe current control circuit is configured to transfer energy from thepower source to the at least one capacitor during a portion of a periodof the varying voltage and from the at least one capacitor to the atleast one LED near the nulls of the varying voltage.
 30. The apparatusof claim 27, wherein the current control circuit is configured to cyclethe at least capacitor at a frequency no greater than twice a frequencyof the varying voltage.
 31. The apparatus of claim 27, wherein thevarying voltage comprises an AC voltage or a rectified AC voltage. 32.The apparatus of claim 27, wherein the current control circuit does notinclude a switchmode power conversion circuit.
 33. A lighting apparatuscomprising: at least one LED; and a current control circuit configuredto provide current to the at least one LED and to at least one capacitorfrom a power source that produces an AC voltage such that energy istransferred from the power source to the at least one capacitor during aportion of a period of the AC voltage and transferred from the at leastone capacitor to the at least one LED near zero crossings of the ACvoltage.
 34. The apparatus of claim 33, wherein the current controlcircuit is configured to cycle the at least one capacitor at a frequencyno greater than twice a frequency of the AC voltage.
 35. The apparatusof claim 33, wherein the light output is constrained to have a minimumlevel of at least 5% of a peak level of the light output.
 36. Theapparatus of claim 33, wherein the current control circuit does notinclude a switchmode power conversion circuit.